1. Field of the Invention
The present invention relates generally to a high-speed packet data communication system, and in particular, to a method and apparatus for applying coded and interleaved data to the input of a turbo decoder.
2. Description of the Related Art
A W-CDMA (Wideband-Code Division Multiple Access) mobile communication system such as CDMA2000 and UMTS (Universal Mobile Telecommunication Service) uses turbo encoding and interleaving to reliably transmit multimedia data at a high rate. It is known that the turbo encoding exhibits very excellent information recovery performance in terms of bit error rate (BER) at a low Signal-to-Noise Ratio (SNR). The interleaving renders adjacent bits to be randomly influenced by fading in a fading environment, thus preventing burst errors and increasing the effect of the channel encoding.
According to an Evolution in Data and Voice (1xEV-DV) standard called CDMA2000 Release C on which the 3rd Generation Partnership Project (3GPP and 3GPP2) are working, a base station (BS) classifies code symbols produced by channel-encoding a packet data stream in a channel encoder into subblocks of a predetermined size according to the types of the code symbols, and interleaves the respective subblocks. A mobile station (MS) recovers the code symbols by deinterleaving the interleaved symbols in the reverse order to the interleaving, and turbo-decodes the code symbols.
1xEV-DV provides that an encoder packet (EP) for the input of the turbo encoder in the BS is 408, 792, 1560, 2328, 3096, or 3864 bits and the maximum number of code symbols transmittable for one unit time of a forward packet data channel (F-PDCH) is limited to 7800. Moreover, code symbols of different types alternate with each other during transmission in order to maximize turbo decoding performance. To accurately recover the data transmitted in the above complicated procedure, a receiver needs buffers for respective operations, involving time delays in buffering.
Random Access Memories (RAMs) are used as these buffers in the MS receiver. In view of sequential input/output at each buffer, as the number of buffers increases, a total data processing time increases significantly. Therefore, efficient buffer management is a significant consideration to designing a MS receiver supporting high-speed data service. Hence, there is a need for a method of recovering turbo decoder input accurately and rapidly in a mobile communication system supporting high-speed data service.